Extlinux.conf is not found, exiting

I just downloaded three files,secureboot_R32.7.2_aarch64.tbz2,Tegra_Linux_Sample-Root-Filesystem_R32.7.2_aarch64.tbz2,Jetson_Linux_R32.7.2_aarch64.tbz2,and untar the same folder Linux_for_Tegra3272,and then run the command sudo ./flash.sh jetson-xavier-nx-devkit mmcblk0p1,the error shows below:
/home/fs/Linux_for_Tegra3272/rootfs/boot/extlinux/extlinux.conf is not found, exiting…

but sdkmanager tools is okey to download system to the SOM, what is problem?

The problem is your steps had something wrong. For example, you didn’t run apply_binaries.sh.

Using rootfs directory of: /home/fs/Linux_for_Tegra3272/rootfs
||||||||||||||||||||||| ERROR |||||||||||||||||||||||

  1. The root filesystem, provided with this package,
    has to be extracted to this directory:
    /home/fs/Linux_for_Tegra3272/rootfs

  1. The root filesystem, provided with this package,
    has to be extracted with ‘sudo’ to this directory:
    /home/fs/Linux_for_Tegra3272/rootfs

Consult the Development Guide for instructions on
extracting and flashing your device.
|||||||||||||||||||||||||||||||||||||||||||||||||||||
sudo ./apply_binaries.sh, why the error?

Is the disk where you stored this rootfs a ext4 partition?

yes , the host system is ubuntu18.04 with ext4 partition

the problem is rootfs permission , I resolve it, thanks